Apparatuses are known, for feeding a metal charge to the melting furnace of a steelworks. Before being fed to the furnace, the metal charge or scrap is normally pre-heated by means of the fumes produced by the melting of the metal.
Some known apparatuses provide a feeding and pre-heating tower for the scrap, integrated with the furnace and disposed directly above it, such as for example in the solution shown in JP 61 015908 A, so that the scrap is discharged from above directly into the liquid bath, with obvious problems, given the quantities of metal charge fed on each occasion, even 40 tonnes, of splashing of the liquid bath and slag, given the height, even 4-5 meters, from which the metal charge is discharged, and also problems of transmission of knocks and vibrations from the tower to the furnace during these steps.
Other apparatuses, known for example from EP-B-1.153.144 and the patent application CA-A-2,222,401 (corresponding to EP 1.034.313), comprise a tower to feed the scrap that is outside and separate from the melting furnace. In this case, for the purposes of pre-heating, the fumes exiting from the furnace are conveyed to the top of the tower where they enter, from the top downward, in the same direction as the scrap to be pre-heated.
In particular, the fumes exit from the melting furnace by means of a pipe that is connected to the top of the pre-heating tower, in which there is also an aperture for the introduction of the scrap using buckets. Selective opening means allow the scrap to progressively descend toward the central part of the tower, where there is the conveyor system that transports the scrap, pre-heated by the fumes that also descend from the upper part to the lower part of the tower, inside the furnace. The fumes continue their descent toward the bottom of the pre-heating tower, where there is a post-combustion chamber.
These known apparatuses have the main disadvantage, however, that the early contact of the fumes with the scrap, given their short journey, does not give the necessary time for completing the combustion of the fumes, which therefore, when they come into contact with the metal charge, are still rich in carbon monoxide because it has not been completely combusted into carbon dioxide. This causes, first of all, the risk of explosions in the metal charge with the danger of compromising the functionality of the process, the integrity of the plant and the safety of the workers. Furthermore, after the pre-heating step there is a presence of carbon monoxide in the fumes directed to the flue, which entails more risks of explosions along the pipes and also the need to provide appropriate and costly systems to remove the carbon monoxide before the fumes are introduced into the atmosphere, since carbon monoxide is notoriously a dangerous and toxic pollutant.
Another disadvantage of known devices is that the metal charge is put in contact with the fumes when they are still very hot, and this risks causing the small-size components of the metal charge and the components that melt at low temperatures to melt already in the first part of the feed tower.
If this melting occurs in the zone where the metal charge is introduced inside the electric furnace, compact blocks are formed that cause blockages in the conveyor pipe, with consequent long and complex interventions to reactivate the plant.
Another disadvantage of known apparatuses is that the fumes which hit the metal charge directly at high temperature, comprised between about 1,200° C. and about 1,350° C., cause high levels of oxidation of the metal charge. The oxidation reduces the yield of the metal charge and frustrates the beneficial effect of recovering the energy of the fumes, since a greater electric energy is required in order to melt the oxidized metal charge in the furnace.
Moreover, the high losses of load that affect the fumes along their path inside the pre-heating chamber have the disadvantage of requiring apparatuses to be installed that have greater power, so as to induce the motion of the fumes from the chamber to the exit flue.
One purpose of the present invention is to obtain an apparatus to feed and pre-heat the metal charge intended for the melting furnace of a steelworks, which pre-heats the metal charge uniformly, exploiting the energy of the fumes exiting from the melting furnace, which fumes, before hitting the metal charge, are processed in order to burn all the carbon monoxide and to remove the particulate present therein.
Another purpose of the present invention is to obtain an apparatus to feed and pre-heat a metal charge which allows to prevent, or at least to limit, the oxidation or melting, even only partial, of the metal charge and which allows to recover energy advantageously in the range of 60-70 kWh/t.
Another purpose of the present invention is to supply a compact apparatus that is not expensive from a construction point of view, and which allows to reduce the expenditure of energy needed to carry out the steel-making processes.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.